The present invention relates to tree debarking devices and specifically to rotary debarker heads.
Wood production typically begins with felling and stripping trees at a logging site. Stripped trees are transported from the forest in large log sections for further processing at a sawmill. The process of stripping a felled tree typically includes removing the bark from the tree which is known as debarking and commonly occurs at the sawmill. A debarking machine having a rotating debarker head is commonly used for the debarking process. Such machines will typically include means for rotating a log under or over a rotating debarker head which travels along the length of the log for removing the bark in preparation for further processing. Such debarking machines will typically have an array of cutting knives, arranged for cutting and chipping bark from the log. The specific arrangement of the cutting knives affects the effectiveness of the debarking process for any given species of log. The most effective arrangement of cutting knives for a hard wood, for example, is different than that for a soft wood. However, a logging site will frequently have only one type of debarker. Thus, the wood processing industry is, as a general rule, faced with the problem of effectively debarking many different species of logs with only one type of debarker.
Debarker heads which are commercially available, commonly use complicated constructions, requiring many parts, including close fitting keyed drive shafts, assembly bolts to hold stacks of cutting elements together on the drive shaft, and set screws to tighten the cutting elements to the drive shaft. A debarker head is subjected to severe torque shock loading, frequently resulting in damaged shaft keyways, keys, and cutting elements. The clamping bolts which hold the cutting elements together and the set screws also sustain frequent damage. Further, the conditions under which debarkers are used subjects the equipment to rust and the components of the debarker head often become fused together. Thus, significant maintenance and repair are often required at the logging site.
The structural arrangement of common heads adds to the difficulty and expense of operating and maintaining a debarking device in the field. Such a debarker head will typically have six to eight cutting elements, each having four to seven wings, stacked on a drive shaft. Each cutting element will have a specific order in the stack, relative to the other cutting elements. Each cutting element will also be keyed relative to the other cutting elements and/or keyed to the drive shaft for a specific rotational position relative to the drive shaft and the other cutting elements. Thus, each cutting element cannot be interchanged with the other cutting elements comprising the debarker head.
Because of this uniqueness of each cutting element, many spare parts must be maintained at the logging site for proper repair and maintenance of the debarker head. In most cases, these heads cannot be repaired in the field. As a practical result, a complete spare debarker head must be available at the site in order to minimize maintenance and repair down time. Conversely, debarking must be suspended while a replacement part is ordered, fabricated and delivered. A third alternative would be to provide the logging site with complete, on demand refabrication facilities. However, each of these alternatives is expensive.